Evaluation of the impact of an in-furrow granular insecticide on rootworm injury to rootworm traited hybrids near Cavour, SD, 2022 Open Access

A corn rootworm (northern corn rootworm/western corn rootworm) management efficacy trial was established on 16 May 2022 near Cavour, South Dakota. Experimental plots were arranged in an randomized complete block design with 4 replications, and each plot was 4 rows wide with 30 inches of spacing between rows by 48 ft in length. Plots were planted using a SRES Seed Pro planter with a seeding rate of 30,800 seeds per acre. Seed corn hybrids without corn rootworm traits (Dekalb (DKC45-95VT2P RIB: VT2P RIB Complete (VT2PRIB) Cry1A.105/Cry2Ab2), Northrup King (NK9023-3220A: Agrisure Viptera 3220 E-Z (VZ) Cry1Ab Cry1F Vip3A), Pioneer (P9211AM AcreMax (AM) Cry1Ab Cry1F) and hybrids with corn rootworm traits (Dekalb (DKC102RM: SmartStax Pro: SmartStax Pro w/RNAi Technology (SSPRORIB) Cry1A.105/Cry2Ab2 Cry1F Cry3Bb1 Cry34/35Ab1 DvSnf7 dsRNA), Northrup King (NK9023-5222A: Agrisure Duracade 5222 E-Z (D2) Cry1Ab Cry1F Vip3A mCry3A eCry3.1Ab), Pioneer (P9211Q: Qrome (Q) Cry1Ab Cry1F mCry3A Cry34/35Ab1)) were used. The Aztec HC 2.1G insecticide was applied at planting time using the SmartBox metering system. The SmartBox insecticide application meter was adapted to fit the Noble meter mounting brackets. Plant stand counts (13 June) and lodging (3 Aug) data were collected from the center 2 rows of each plot. Stand was determined by counting the number of plants in 17.5 feet of row (1/1,000th of an acre) and percent lodging was calculated as the total number of plants in the row that were at a 30-degree or greater angle divided by total number of plants in the row. Root rating means were derived from 6 roots dug randomly from the 2 outer rows at growth stage tassel growth stage on 19 Jul. Roots were washed then rated for severity of rootworm feeding injury using the Oleson 0 to 3 root injury scale. Yield assessments in bushels per acre were taken from the center 2 rows of the 4 row plots on 24 Oct. Yield data was analyzed by seed company to avoid comparing hybrid differences. Plant stand, root rating, lodged plants, and yield were analyzed using analysis of variance means separation according to Duncan’s New Multiple Range Test in the ARM research management software.

Corn root injury from rootworm feeding in the 3 untreated checks exceeded the ~ 0.25 EIL (Table 1). The Pioneer AM non rootworm traited hybrid had 2.02 nodes of root injury and the addition of AztecHC 2.1G significantly decreased damage by 1.88 nodes of injury. The AztecHC 2.1G significantly reduced the root rating injury for the Dekalb VT2P non rootworm traited hybrid from 2.43 to 0.1. The Agrisure Viptera was also heavily injured with a root rating of 2.21 but root injury was significantly reduced by AztecHC 2.1G to 0.10. The Pioneer Qrome, Dekalb SmartStax Pro, and Northrup King Duracade rootworm resistant hybrids all provided adequate root protection from larval feeding and no significant differences for root injury were detected with the addition of AztecHC 2.1G for these hybrids. These traited hybrids had root ratings of 0.13 or less which is well below the 0.25 economic injury level. Although root injury was not significant, the addition of AztecHC 2.1G to the Syngenta Viptera non rootworm resistant hybrid significantly improved the yield with a 1.6-fold bushel per acre advantage. The Pioneer AM and Dekalb VT2P with an insecticide had a 1.1 and 1.02-fold decrease bu/acre. The rootworm traited Qrome hybrid had a 1.2-fold bu/acre yield increase with the addition of AztecHC 2.1G. However, this was not true for the Dekalb SmartStax Pro or Syngenta Duracade which had a 1.05 and 1.2-fold decreased yield. These results indicate that the inclusion of AztecHC 2.1G at the tested location provided root protection in the absence of rootworm resistance traits.¹

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